This invention relates generally to elastomer type seal boots for universal joints and more particularly to elastomer type seal boots that are made of a thermoplastic elastomer for constant velocity universal joints that stroke.
There are generally two kinds of elastomer type seal boots for universal joints depending upon the elastomer of which the seal boots are made. One kind is the rubber type where the seal boot is made of a natural or synthetic rubber, such as neoprene. The other kind is the plastic type where the seal boot is made of a thermoplastic elastomer, such as HYTREL, a segmented polyester-polyether copolymer type of thermoplastic elastomer that is marketed by E.I. DuPont deNemours and Company of Wilmington, Del.
Plastic seal boots are usually produced by an extrusion or injection blown process. They are generally thinner and lighter than the rubber seal boot but are generally less flexible. Consequently, plastic seal boots are constructed as a conically shaped bellows type structure having a large number of convolutes serially arranged end-to-end between a large diameter mounting skirt and a small diameter mounting ring for attaching the plastic seal boot to the universal joint. The convolutes are generally of equal length and of uniformly decreasing diameter with an enlarged convolute contiguous the large diameter mounting skirt. See for instance U.S. Pat. No. 4,735,596 granted to Mikio Ukai et al Apr. 5, 1988, which discloses a "conventional" plastic seal boot for a stroking constant velocity universal joint in FIGS. 1 and 2 that is shaped like a conical bellows comprising has a plurality of equal length convolutes of uniformly decreasing diameter interposed between large and small diameter mounting rings.
Attempts have been made to improve the stress distribution in the "conventional" plastic seal boot and thereby increase its durability and life. See for instance the Ukai patent discussed above and U.S. Pat. No. 4,844,486 granted to Wolfram Schiemann Jul. 4, 1989 for an oil and grease-proof bellows for enclosing joints on axles of motor vehicles. These past attempts propose to increase durability and life by modifying one or more convolutes, particularly the convolute adjacent the small diameter mounting ring while retaining the large regular conical shape of the plastic seal boot.